The present invention is a new design for an internally threaded fastener. It is similar to other fasteners, called "rivet nuts", because it includes characteristics of both a rivet and a nut. Parts to be joined become trapped (riveted) between the head and the collapsible middle portion of the fastener shank which bulges radially outward, being deformed by compression as a screw threaded into the fastener shank is tightened. Later, other parts may be joined to the riveted subassembly by a headed screw driven into the fastener's internal threads. An example of this type of fastener is disclosed in U.S. Pat. No. 5,065,283 issued to Adachi et al. This reference shows leads of a busbar attached to a circuit board with the use of a rivet nut type fastener.
The specific application to which the present invention is most advantageously applied is in the circuit board component assembly arts. U.S. Pat. No. 4,911,659 issued to Viselli shows the use of metal retaining brackets to affix a plastic connector housing to a circuit board. The mounting brackets disclosed in this patent include metal shanks which are peened over to secure mounting ears of the housing to the bracket. In modern practice, however, separate mounting brackets are eliminated in favor of connector housings (made of plastic) with mounting brackets molded into the body of the housing. This creates new problems for fasteners used in the electrical connector assembly, since the connector fasteners now must be applied directly to a plastic part, rather than a metal bracket.
Greater background of the specific application of the present invention described above is shown in FIG. 1 which depicts a prior art electrical connector assembly utilizing fasteners applied directly to a plastic housing. Housing 11 includes molded-in brackets which provide mounting points to both the printed circuit board and the connector assembly. The electrical connector assembly includes interlocking shells 13a and 13b which are joined to the vertical portions of the housing mounting brackets by the use of internally threaded fasteners 17. Jack screws 19 secure panel 15 to the assembly and provide securement for the electrical connector plug, which is not shown in this figure. Female fasteners 17 are affixed to housing brackets 10 by broaching the shanks into the plastic material around the bracket apertures.
While this method creates a simplified assembly, it poses production problems and limitations upon the connector fasteners. For example, many of the housings become damaged when the fasteners are broached into the plastic part. Furthermore, the pullout resistance of the fasteners is limited by the inherent weakness of the broached plastic. Also, the fasteners need to be relatively short because of the broach insertion and this limits the amount of threads in the fastener bore. Lastly, when removing the connector assembly from a mounting panel, the jack screw often turns with the mating cable end connector and the board-mounted connector can accidentally become disassembled.
There is therefore a need in the art for a fastener and fastening system for joining metal and plastic parts which provides a strong joinder of parts without damage to the plastic element. Furthermore, there is need for such a fastener which also includes self-locking threads.